1. Technical Field
The present invention relates to a semiconductor device and a method of fabricating the same, and in particular to a semiconductor device containing an electric fuse and a method of fabricating the same.
2. Related Art
There has been known a technique of mounting a fuse on a semiconductor device, and blowing the fuse so as to adjust values of a resistor used for the semiconductor device, or to disconnect a nonconforming element for replacement with a normal element.
Laser irradiation to a position of blowing of the fuse is one of known methods of blowing the fuse. Japanese Laid-Open Patent Publication No. H11-297837 discloses a technique of solving the problems below anticipated about the fuse blown by laser. That is, as the design rule of semiconductor devices shrinks, interconnections to be disconnected also shrink, so that there is a growing demand on a higher level of positioning accuracy in the laser irradiation, for a laser repair apparatus used for blowing the fuse interconnection. However, use of a new apparatus for every product of a new generation results in endless increase in the production cost. Aiming at providing a technique of exactly blowing the fuse using a former-generation laser repair apparatus having only a limited level of positioning accuracy, Japanese Laid-Open Patent Publication No. H11-297837 proposes a circuit configuration having a plurality of interconnections to be disconnected for switching a single internal circuit, allowing switching of the circuit only if either one of the plurality of interconnections is disconnected. It was reportedly made possible to reduce any opportunities of switching failure of the circuits, due to misalignment of a laser beam onto the interconnection to be disconnected.
On the other hand, unlike the blowing of fuse based on the laser irradiation, there is known another method of blowing the fuse by current supply (Japanese Laid-Open Patent Publication Nos. 2005-39220 and 2005-57186). Japanese Laid-Open Patent Publication No. 2005-39220 discloses a fuse which can be blown by a smaller energy of current. According to the Publication No. 2005-39220, a conductor composing the fuse is formed as being folded a plurality of times.
Japanese Laid-Open Patent Publication No. 2005-57186 discloses a configuration in which a fuse is surrounded, specifically in the portion to be blown, by a plate so as to confine heat generated in the portion to be blown within an area at around that portion, when current is supplied to the fuse.
The current-disconnection-type fuse (E fuse, referred to as electric fuse, hereinafter), blowing the fuse by supplying thereto a predetermined energy of current, is intrinsically free from a problem in positioning accuracy which is anticipated in the system blowing the fuse by laser irradiation.
The electric fuse, however, is in need of further improvement in the yield ratio of disconnection. It was also found that the electric fuse has arisen some new problems.
The electric fuse may be re-connected in the portion once it was blown, if blowing of the electric fuse is followed by annealing. In particular for the case where the electric fuse is composed of a material causative of electro-migration, it is anticipated that the portion once blown may be re-connected as being affected by electro-migration of the material, when the blowing of electric fuse is followed by annealing. Once such re-connection should occur, detection of whether the electric fuse has been blown or not cannot give a correct result, even if the electric fuse to be blown is once disconnected.
Although incidence of the re-connection or re-disconnection described in the above may actually be not so large, so that use of the electric fuse may be supposed as being of no problem so far as the fuse is adopted to normal operations, it is still necessary to further improve the hold characteristic, a capability of the electric fuse holding the blown state, for the case where an extremely advanced level of reliability is demanded for the semiconductor device, or for the case where the semiconductor device is used under severe conditions.